1. Field of the Invention
This invention generally relates to the manufacture of a wound ball, typically a wound golf ball comprising a core having rubber thread wound on a spherical center and a cover on the core. More particularly, this invention relates to a method and apparatus for winding rubber thread on the center to form the wound core.
2. Prior Art
In general, wound golf balls are manufactured by winding rubber thread around a center, which is either a liquid center in the form of a rubber bag filled with a liquid or paste or a solid center made of solid rubber, to form a wound core, and enclosing the core with a cover.
It is a common practice to wind rubber thread on a center by holding the center among a plurality of rotatable winding rollers, feeding rubber thread to the surface of the center, and driving at least one of the winding rollers for rotation to thereby winding the :rubber thread around the center. After rubber thread is wound on the center by this method, a trailing end of rubber thread must be secured to the wound core. The following techniques are known and used for securing the trailing end to the wound core.
(1) The trailing end of rubber thread is placed on the surface of the wound core and adhesive is applied thereat to adhesively bond the trailing end to the wound core surface. See Japanese Patent Publication (JP-B) No. 49985/1986.
(2) A trailing section of rubber thread is wound two or three turns on the wound core such that the trailing end is interposed between the center surface and the turns of rubber thread, thereby binding the trailing end to the wound core.
These trailing end securing techniques, however, have the following problems. The adhesive technique (1) has the following problems. (i) After a droplet of the adhesive is applied, it is dried and cured over a certain time. (ii) Due to tackiness of the adhesive, foreign matter is likely to adhere thereto. (iii) The winding apparatus is contaminated with the adhesive and its maintenance becomes cumbersome. (iv) Application of adhesive is not effective in the case of a liquid center because the liquid center is frozen before winding of rubber thread. While the center is allowed to thaw at the end of winding, moisture condenses on the wound rubber to prevent the adhesive from performing well. (v) The adhesive is eventually left in the ball to alter its performance.
Technique (2) of binding rubber thread to the wound core is free of the problems associated with the adhesive, but is currently carried out by manual operation because of difficulty of automation. The manual binding operation is cumbersome and requires skill, contributing to an efficiency reduction in the manufacture of wound golf balls.
Referring to FIG. 12, technique (2) of binding rubber thread to the wound core is illustrated in more detail. The worker holds a wound core a with fingers (only one finger shown in FIG. 12A) and winds a trailing section of rubber thread a few turns on the wound core over the fingers as shown in FIG. 12A. At the end of this operation, the trailing end c of rubber thread is pressed with the finger as shown in FIG. 12B. The finger is then withdrawn from inside the rubber thread turns while pulling the trailing end c to come under the thread rubber turns as shown in FIG. 12C. As a result, the trailing end c is interposed or bound between the rubber thread turns and the wound core a as shown in FIG. 12D. In this way, the trailing end c of rubber thread is secured to the wound core a.
After the wound core is manually taken out of the winding apparatus, the above-mentioned cumbersome rubber thread binding operation is carried out while paying attention not to allow the already wound section of rubber thread to loosen. This operation is inefficient and the binding operation can be performed only by a skilled worker who has subtle fingers. It is very difficult for an automatic robot machine to perform the binding operation.
The prior art winding methods are not fully satisfactory with respect to efficient manufacture and quality reliability of products because many problems arise in securing the trailing end of rubber thread to the wound core. There is a desire to have a winding method which can solve the problems associated with the end of rubber thread winding and produce wound golf balls of quality in an efficient manner.